Stabilization of fuel oil



i atent f fiice srAnrLrzArroN or FUEL on.

Harold Beuther and Richard G. Goldthwait, PennTowm ship, Allegheny County, Pa, assignors to Gulf Research & Development Company, Pittsburgh, 1%., a corporation of Delaware No Drawing. Application .iuly 2, 1953, erial No. 365,764

9 Claims. (Cl. 1%5tl) This invention relates to-a process for the stabilization of fuel oils and moreparticularly for stabilizing fuel 'oils prepared from severely vis-broken residues of petroleum crudes.

In the normal refining of petroleum crudes, the crude oil is first subjected to an atmospheric distillation process in which gas oil and lighter fractions are recovered as distillate products and a heavy virgin residue is withdrawn as a bottoms product. In some refineries the virgin residue is blended directly with a relatively light oil of low viscosity, ordinarily a refractory cycle stock from thermal or catalytic cracking operations commonly referred to as a cutter oil, to the proper viscosity for a heavy fuel oil. With the increased use of catalytic cracking processes, vacuum distillation of the bottoms from the atmospheric distillation step to increase the virgin stock available for charging to the catalytic cracking process has become more widely used. In this manner, the amount of residual products used in the preparation of fuel oil is diminished as compared with atmospheric distillation; however, larger amounts of cutter oil are required to blend the residue from the vacuum distillation to produce a fuel oil ofacceptable viscosity.

The heavy fuel oils to which this invention relates are usually identified as No. 6 fuel oil. The Ass. T. M. Standards Designation D396-48T provides that a No. 6 fuel oil should have a Saybolt Furol viscosity at 122 F. of 45300 seconds, and the stabilization of fuel oils of this type is an object of this invention.

Some refineries subject the bottoms from the distillation of the crude oil to a mild, single pass, thermal cracking operation known asvisbreaking. The visbreaking reduces the viscosity of the bottoms, thereby decreasing the cutter oil requirements for blending to a fuel oil of suitable viscosity. In addition, a mildly cracked distillate suitable for charging to catalytic cracking or a more severe thermal cracking is recovered, together with an appreciable yield of gasoline.

The advantages of greater reduction ofviscosity of the residue and the reduction in the cutter oil requirements are, in general, increased with increasing severity of the thermal cracking conditions employed in the visbreaking. Howevenfuel oils prepared from severely visbroken residues are lacking in stability and compatibility with the cutter'oil. The instability of the fuel oil may be evidenced'by an increase in'viscosity of the fuel oil when stored for extended periods, stratification of the fuel oil into two liquid phases of different viscosities, and the'separation ofa sludge from the fuel oil. In extreme cases, the fuel oil may tend to congeal to a jelly-likeconsistency. Another disadvantage of unstable fuel oils is their tendency to deposit solid carbonaceous material on heating surfaces over which the'fuel oil passes. Since it is generally necessary to handle the fuel oil at elevated temperatures, the carbon deposition causes serious difiiculty in burners,'nozzles, lines and valves.

Attempts have been made to improve the characteristics of the fuel oils by'filtration of solid sediment from the oil and by the addition of solvents designed to dissolve the sediment. These procedures have not been successful either because of failure to accomplish the desired-objective or because of the high cost. The No. 6-f11el"oils normally have a very low market price and often must be sold on a distressed market; hence, an acceptable process for improving their stability cannot add materially to the cost of the fuel oils.

Unstable fuel-oils prepared from severely visbroken residues of petroleum crudes are stabilized, according to this invention by the additionthereto--of--heavy,--high boiling portions-of virgin crudes from the at'rnosphericor vacuum distillation of petroleum crudes. The fuel oil resulting from the mixture of the unstable visbroken fuel oil with the heavy, high-boilingpoint virgin fractions must have a viscosity within the specifications. "Adjustrnent of the viscosity of the mixture may'be madeby blending therewith a cutter oil, either before or after the mixing of the unstable visbroken fuel oilwith the highboiling virgin fractions. The minimum total volume of the virgin residue audits attendant cutter oil added to the unstable fuel oil to obtain-a stabilized fuel oil of the desired viscosity should be approximately'equal to the volume of the unstable visbroken fuel oil.

The visbroken fuel oils which are stabilized according to this invention are derived from severely visbreaking, by a single pass thermal cracking process, the bottoms from a deep vacuum reduction of a crude'oil. The'severity of the visbreaking'may be'measured by the yield'of gasoline. In general, an unstable fuel oil' will result ifthebo'ttoms are visbroken at conditions sufficiently severe to yield more than about 9%, 400 F. end point, debutanized gasoline. The minimum severity of visbreaking, as indicated by yield of gasoline, will depend on the typeof crude oil, and, in some instances, unstable fuel'oilsmay not be encountered until'gasoline yields above 11 or "12% are obtained. Generally, less stable fuel 'oils are derived from crudes having high asphaltene contents than from crudes low in asphaltenes, 'whenjthebottoms'from distillation of the respective crudes are visbroken at comparable 'severities.

As mentioned above, conventionalvisbreaking processes employ mild cracking conditions. If conventional visbreaking feed stocks are cracked at higher'severties, the formation of coke is excessive. Inapplication 'Serial No. 262,566 of Harold BeutherfWilliam C. Oifuttand Paul-Siekea process is described and claimed which-allows visbreaking at greatly increased severities without excessivec'oking. In that process; the'petroleum crude "is very deeply reduced by vacuum distillation to form a residual product having a gravity below 10 A. P. 1., a Conradson carbon residue above 18, and an SUS'viscosity at 210 F. above 6000. It hasbeen'discovered that contrary to the teaching of the. prior art, the very heavy residual product may be cracked at high severities without excessive coke formation. However, the increased conversion of the very heavyhigh-boiling' fractions made possible by the earlier invention, will result'in unstable fuel oils if the severity of 'visbreaking is such as to yield at least about 9%, 400 Rendpoint, debutanized gasoline.

In general, the virgin residue used to stabilize the visbroken fuel oils may'be obtainedfrom any petroleum crude oil having a gravity above about 15 A. P. I. Among the crudes which are suitable-for this invention are those from West Texas, Mid-Continent, Kuwait, East Texas, Coastal and Ordovician fields. Venezuelan crude oils, other than the heavy tar sand oils, are also suitable.

It is'believed that the heavy oils present in virgin crude oil residues exert a peptizing efiect 'onthe heavy asphaltic materials in the visbroken fuel oils to keep them in solution. There may also be an additional stabilizing effect,

oils prepared by topping petroleum crude oils and storage stability tests run on the blends. The viscosity of the blends was determined at the beginning of the storage period and again after the blended fuel oils had been in storage for a period of three months. The test was further extended to a total period of one year and the viscosity determined again at the end of that period. Separate blanks of 100 per cent virgin fuel oil and 100 per cent visbroken fuel oil were tested in a similar manner for comparison with the blended fuel oils. The results of the storage tests are set forth in Table I.

Table I.E'flect of blending virgin fuel oil with visbroken fuel oil on stability and compatibility 100 Vir in 907 Virgin 50% Virgin 10% Virgin Virgh Blend Composition "i 0% z isbroisen isbroken 50% visbroken 90% vi b k zy v a Crude Source A B C D E F D E F D E F D E F Fuel Oil Inspections:

Viscosity, Furol at 122 F.,

1 155181 23S 77 184 209 S0 172 178 93 150 256 143 196 221 173 173 After Three Months 230 180 200 82 159 188 91 146 305 123 166 380 200 200 O Y. l lnriiixed i 231 79 176 205 84 182 192 04 155 340 142 208 394 184 lS-l RemixetL 24s 187 217 88 207 108 161 440 22 257 601 500 m0 Vlsgositg lilrereaset 1h t I1117r ee 11 1a isos ii ia i fiiiihi s -2 4 +5 -7.5 +6 +19 1 +72 ViscosityP Increase} fillitstlarl Q ne a 15- i y i- +1 +7.5 +72 +505 +31 +217 59 A-51.0% reduced Kuwait crude. Gravity=15.3 A. P. I. B-Reduced West Texas. Gravity=15.4 A P. I.

C35.7% reduced West Texas crude. Grav1ty=l7.5 A. P. I. D-A-l-Fuel oil from Example 1.

E-B-l-Fuel oil from Example 2.

F-O+Fuel oil from Example 2.

oil of the desired viscosity may be prepared by blending the virgin residue with a lighter fraction, such as a No. 2 or domestic heating oil, or by merely topping a crude oil to separate a longer cut as bottoms, in which event sufficient lighter oils remain with the virgin residues to yield a No. 6 fuel oil.

The preferred method of blending the virgin residue with the unstable visbroken fuel oil is first to blend the virgin residue with a cutter oil to form a virgin fuel oil, and then mix the virgin fuel oil with the visbroken fuel oil to be stabilized. Similarly, a topped crude may be mixed with the unstable fuel oil to produce a fuel oil directly. Another procedure which may be used is to mix a virgin residue directly with the unstable visbroken fuel oil, or with the visbroken bottoms from which the unstable fuel oil is prepared, and then cut the resulting mixture to the desired viscosity with a cutter oil.

EXAMPLE 1 A residue from a vacuum distillation of a Kuwait crude, constituting 17.2 per cent of the crude, was visbroken in a single pass operation with a furnace outlet temperature of 950 F. to yield 14.2 per cent debutanized 400 F. end point gasoline. The naphtha-free bottoms from the visbreaking were blended with a light catalytic cycle stock from a TCC (moving catalyst bed) cracking process in proportions of 14.8 parts naptha-free bottoms to 6.0 parts of light cycle stock to form a visbroken fuel oil.

EXAMPLE 2 A residue from a vacuum distillation constituting 9.9 per cent of a West Texas crude was thermally cracked in a single pass operation at a furnace outlet temperature of 960 F. to yield 12.1% debutanized 400 F. end point gasoline. A fuel oil was prepared by blending the napthafree visbroken bottoms with a light catalytic cycle stock in a ratio of 8.7 parts of naptha-free bottoms to 2.6 parts of light catalytic cycle stock.

The visbroken fuel oils prepared in Examples 1 and 2 were blended in various concentrations with virgin fuel It will be seen from Table I that blends of fuel oil containing substantial proportions of virgin and visbroken fuel oils increase in viscosity over a storage period of one year far less than the visbroken fuel oil and much less than would be expected merely from a blending operation. Mixtures of 50 per cent virgin fuel oil and 50 per cent visbroken fuel oil are satisfactory, both from the stand point of a relatively low increase in viscosity during the storage period of one year and the lack of separation into different layers, as indicated by the close agreement in the viscosity of the unmixed and remixed samples. While some samples of the 10 per cent virgin fuel oil and per cent visbroken fuel oil blend showed only a small increase in viscosity during a three-month storage period, those samples showed distinct separation of layers after one year.

We claim:

1. A process for the stabilization of No. 6 fuel oils prepared from naphtha-free bottoms of residues of petroleum crude oils, said residues having been visbroken at severities yielding at least about 9 per cent gasoline, comprising adding thereto an approximately equal amount of a virgin fuel oil comprising a mixture of a virgin residue and a cycle oil.

2. A process for the preparation of a stable N0. 6 fuel oil comprising vacuum reducing a petroleum crude to form a residue having a Conradson carbon residue number of at least 18, a gravity below 10 API and a viscosity SUS, at 210 F., of at least 6000, visbreaking the residue at a severity yielding at least about 9 per cent gasoline, blending the naphtha-free bottoms from the visbreaking to a specification fuel oil by the addition of a cutter oil, and adding to the fuel oil a virgin residue in an amount limiting the increase in viscosity in storage in a period of one year to about 20 per cent.

3. A process for the stabilization of a visbroken No. 6 fuel oil prepared from a cutter oil and the naphtha-free bottoms from visbreaking a residue of a West Texas crude at severities yielding at least about 9 per cent gasoline, said residue having a Conradson carbon residue number of at least 18, a gravity below API and an SUS viscosity at 210 of at least 6000, and blending the visbroken fuel oil with at least about an equal volume of fuel oil prepared from a virgin residue of a petroleum crude having a gravity above about API.

4. A process for the stabilization of a visbroken No. 6 fuel oil prepared from a cutter oil and the naphtha-free bottoms from visbreaking a residue of a Kuwait crude at severities yielding at least about 9 per cent gasoline, said residue having a Conradson carbon residue number of at least 18, a gravity below 10 API and an SUS viscosity at 210 of at least 6000, and blending the visbroken fuel oil with at least about an equal volume of fuel oil prepared from a virgin residue of a petroleum crude having a gravity above about 15 API.

5. A process for the stabilization of a visbroken No. 6 fuel oil prepared from a cutter oil and the naphtha-free bottoms from visbreaking a residue of a Mid-Continent crude at severities yielding at least about 9 per cent gasoline, said residue having a Conradson carbon residue number of at least 18, a gravity below 10 API and an SUS viscosity at 210 of at least 6000, and blending the visbroken fuel oil with at least about an equal volume of fuel oil prepared from a virgin residue of a petroleum crude having a gravity above about 15 API.

6. A method of stabilizing a thermally cracked fuel oil having a Saybolt Furol viscosity at 122 F. of 45-300 seconds, said cracked fuel oil having been prepared from a cutter oil and naphtha-free bottoms of residues of petrofuel oil, the virgin fuel oil containing virgin residual fractions from petroleum crude oils having a gravity above about 15 API and lighter hydrocarbon fractions to cut the viscosity substantially to the range of the cracked fuel oils.

8. A process for preparing a stable fuel oil having a viscosity in the range of 45-300 Saybolt Furol seconds at 122 F. comprising deeply vacuum reducing a petroleum crude oil to form a residue having a gravity below 10 API, an SUS viscosity at 210 F. of at least 6000, and a Conradson carbon residue number of at least 6000, thermally cracking the residue in a one-pass operation at a severity to yield at least 9 per cent gasoline, distilling the cracked residue to yield naphtha-free bottoms, and mixing the naphtha-free bottoms with virgin residue from a petroleum crude oil having a gravity of at least 15 API and a cutter oil, the amount of the virgin bottoms being sufficient to limit the increase in viscosity upon storing for a period of one year to about 20 per cent.

9. A stable fuel oil composition having a viscosity of 25300 Saybolt Furol seconds at 122 F. comprising naphtha-free bottoms of a petroleum residuum thermally cracked to yield at least about 9 per cent gasoline, cutter oil in amounts which when mixed with the naphtha-free bottoms gives a visbroken fuel oil having a viscosity of 25-300 Saybolt Furol seconds at 122 F. and a virgin fuel oil comprising a virgin residue of a petroleum crude oil having a gravity above about 15 API and a cutter oil, the virgin fuel oil being at least about 50 per cent by leum crude oils which have been severely visbroken to volume of the composition yield at least 9 per cent gasoline, comprising adding topped crudes from petroleum crude oils having a gravity of at least about 15 API, the volume of the topped crude being about at least the volume of the cracked fuel oil.

7. A method of stabilizing a cracked fuel oil having a 2416608 Saybolt Furol viscosity at 122 F. of -300 seconds, said cracked fuel oil consisting essentially of a cutter oil and the naphtha-free bottoms from thermally cracking residues of a petroleum crude oil at severities to yield at least 9 per cent gasoline, comprising adding a virgin fuel 40 oil to the cracked fuel oil, the volume of the virgin fuel oil being at least about equal to the volume of the cracked References Cited in the file of this patent UNITED STATES PATENTS Brackenbury Feb. 25, 1947 2,417,236 Cato Mar. 11, 1947 2,663,675 Ewell Dec. 22, 1953 2,664,388 Winterhalter Dec. 29, 1953 OTHER REFERENCES Schmidt: Fuel Oil Manual, 1951, pages 48, 67 and -122. 

1. A PROCESS FOR THE CONVERSION OF NORMALLY LIQUID PREPARED FROM NAPHTHA-FREE BOTTOMS OF RESIDUES OF PETROLEUM CRUDE OILS, SAID RESIDUES HAVING BEEN VISBROKEN AT SEVERITES YIELDING AT LEAST ABOUT 9 PER CENT GASOLINE, COMPRISING ADDING THERETO AN APPROXIMATELY EQUAL AMOUNT OF A VIRGIN FUEL OIL COMPRISING A MIXTURE OF A VIRGIN RESIDUE AND A CYCLE OIL. 